This invention relates to a zwitterion polymer for water borne coatings. In a particular aspect it relates to a thermosetting zwitterion polymer derived from a cyclic acid anhydride.
Increasingly stringent limitations on the emission of volatile organic compounds into the atmosphere have led to the development of "water soluble" industrial baking enamels. Typically the vehicle in such a system is an acrylic or polyester resin with pendant hydroxyl and carboxylic acid groups. The resins are generally prepared as high solids solutions in a cosolvent (in ether-alcohol or alcohol) and partially neutralized with an amine such as 2-N,N-dimethylaminoethanol or 2-amino-2-methyl-1-propanol (AMP). Usually a melamine-formaldehyde resin such as hexamethyoxymethylmelamine (HMMM) is used as a cross-linking agent. The system is diluted to application viscosity with water. During cure at least part of the amine is volatilized and crosslinking between HMMM and the resin occurs. Under emission control regulations, the volatilized amine must be included as a volatile organic compound and hence is objectionable. Also, it has been reported that some secondary and tertiary amines undergo photochemical reactions under atmospheric conditions to yield nitrosamines and nitramines. It would, therefore, be desirable to have a similar system in which amine would not be volatilized during cure.